June 17, 2008

Two weeks ago Tyson Foods Inc. killed and buried the carcasses of 15,000 hens in northwest Arkansas that tested positive for exposure to a strain of the avian flu that is not harmful to humans, state officials announced.

The affected chickens had antibodies of a mild or low pathogenic strain of bird flu called H7N3.

It is the deadly high pathogenic H5N1 strain, which has never been found in the United States, that worries scientists because it has spread to and killed people around the world.

The deadly H5N1 strain has spread to humans overseas who have been in close contact with infected chickens. So far there have been 376 human cases worldwide including 238 deaths.

A major worry among health experts is the H5N1 strain will mutate into a form that can be transmitted from human to human, raising the threat of a global pandemic that could kill millions.

Jon Fitch, director of the state’s Livestock and Poultry Commission, said routine blood tests conducted on May 30 found the possible exposure. Further tests done by the state and the U.S. Department of Agriculture found the birds did not have active infections, but rather were exposed to a subtype of the disease.

“Even though the affected birds do not currently have the virus, the flock is being depopulated today as a precautionary measure and will not enter the human food chain. While the birds’ exposure to this strain of avian influenza poses no risk to human health, USDA’s policy is to eradicate all H5 and H7 subtypes,” the company, based in Springdale, Arkansas, said in a statement.

Fitch said the company immediately began disposing of the birds.

“There is absolutely no human health threat,” Fitch said. “But we take this very seriously.”

“Honestly, it’s a nonevent. So far, it’s not something that’s reportable to any international monitoring agency like the World Organization for Animal Health,” said Toby Moore, spokesman for the USA Poultry and Egg Export Council, an industry trade group.

Fitch said state officials decided against announcing the infection to the general public because the birds tested positive for exposure to the H7N3 strain of the virus. The strain that ravaged Asian poultry stocks in late 2003 was H5N1 bird flu virus.

Gary Mickelson, a spokesman for Springdale-based Tyson, said the hens showed no signs of sickness before their pre-slaughter blood tests. He said the exposed birds all came from a contractor.

“As a preventive measure, Tyson is also stepping up its surveillance of avian influenza in the area,” Mickelson said in a statement. “The company plans to test all breeder farms that serve the local Tyson poultry complex, as well as any farms within a 10-mile radius of the affected farm.”

Following the discovery, the U.S. Agriculture Department suspended shipments of chicken from Arkansas to Russia, the most important overseas market for U.S. chicken.

The United States has bilateral agreements with Russia and Japan to report any finding of avian influenza strains H5 or H7, said Rachel Iadicicco, spokeswoman for U.S. Animal and Plant Health Inspection Service. Upon notification of a find, the United States automatically suspends the state’s exports to Russia, and Japan voluntarily decided to implement its ban, Iadicicco said.

There have been previous cases of mild bird flu in the United States. Last year government investigators found cases in 13 states.